168 notecards = 42 pages (4 cards per page)
Acetyl coenzyme A; the entry compound for the citric acid cycle in cellular respiration, formed from a two-carbon fragment of pyruvate attached to a coenzyme.
A catabolic pathway for organic molecules, using oxygen ( O 2 ) as the final electron acceptor in an electron transport chain and ultimately producing ATP. This is the most efficient catabolic pathway and is carried out in most eukaryotic cells and many prokaryotic organisms.
Glycolysis followed by the reduction of pyruvate to ethyl alcohol, regenerating NAD+ and releasing carbon dioxide.
A complex of several membrane proteins that functions in chemiosmosis with adjacent electron transport chains, using the energy of a hydrogen ion (proton) concentration gradient to make ATP. ATP synthases are found in the inner mitochondrial membranes of eukaryotic cells and in the plasma membranes of prokaryotes.
A metabolic sequence that breaks fatty acids down to two-carbon fragments that enter the citric acid cycle as acetyl CoA.
The catabolic pathways of aerobic and anaerobic respiration, which break down organic molecules and use an electron transport chain for the production of ATP.
An energy-coupling mechanism that uses energy stored in the form of a hydrogen ion gradient across a membrane to drive cellular work, such as the synthesis of ATP. Under aerobic conditions, most ATP synthesis in cells occurs by chemiosmosis.
citric acid cycle
A chemical cycle involving eight steps that completes the metabolic breakdown of glucose molecules begun in glycolysis by oxidizing acetyl CoA (derived from pyruvate) to carbon dioxide; occurs within the mitochondrion in eukaryotic cells and in the cytosol of prokaryotes; together with pyruvate oxidation, the second major stage in cellular respiration.
An iron-containing protein that is a component of electron transport chains in the mitochondria and chloroplasts of eukaryotic cells and the plasma membranes of prokaryotic cells.
electron transport chain
A sequence of electron carrier molecules (membrane proteins) that shuttle electrons down a series of redox reactions that release energy used to make ATP.
facultative anaerobe (fak′-ul-tā′-tiv an′-uh-rōb)
An organism that makes ATP by aerobic respiration if oxygen is present but that switches to anaerobic respiration or fermentation if oxygen is not present.
A catabolic process that makes a limited amount of ATP from glucose (or other organic molecules) without an electron transport chain and that produces a characteristic end product, such as ethyl alcohol or lactic acid.
A series of reactions that ultimately splits glucose into pyruvate. Glycolysis occurs in almost all living cells, serving as the starting point for fermentation or cellular respiration.
lactic acid fermentation
Glycolysis followed by the reduction of pyruvate to lactate, regenerating NAD+ with no release of carbon dioxide.
The oxidized form of nicotinamide adenine dinucleotide, a coenzyme that can accept electrons, becoming NADH. NADH temporarily stores electrons during cellular respiration.
The reduced form of nicotinamide adenine dinucleotide that temporarily stores electrons during cellular respiration. NADH acts as an electron donor to the electron transport chain.
obligate anaerobe (ob′-lig-et an′-uh-rōb)
An organism that carries out only fermentation or anaerobic respiration. Such organisms cannot use oxygen and in fact may be poisoned by it.
The complete or partial loss of electrons from a substance involved in a redox reaction.
oxidative phosphorylation (fos′-fōr-uh-lā′-shun)
The production of ATP using energy derived from the redox reactions of an electron transport chain; the third major stage of cellular respiration.
The electron acceptor in a redox reaction.
proton-motive force (prō′-ton)
The potential energy stored in the form of a proton electrochemical gradient, generated by the pumping of hydrogen ions (H+) across a biological membrane during chemiosmosis.
redox reaction (rē′-doks)
A chemical reaction involving the complete or partial transfer of one or more electrons from one reactant to another; short for reduction-oxidation reaction.
The electron donor in a redox reaction.
The complete or partial addition of electrons to a substance involved in a redox reaction.
The enzyme-catalyzed formation of ATP by direct transfer of a phosphate group to ADP from an intermediate substrate in catabolism.
The amount of energy that reactants must absorb before a chemical reaction will start; also called free energy of activation.
The specific region of an enzyme that binds the substrate and that forms the pocket in which catalysis occurs.
The binding of a regulatory molecule to a protein at one site that affects the function of the protein at a different site.
anabolic pathway (an′-uh-bol′-ik)
A metabolic pathway that consumes energy to synthesize a complex molecule from simpler molecules.
ATP (adenosine triphosphate) (a-den′-ō-sēn trī-fos′-fāt)
An adenine-containing nucleoside triphosphate that releases free energy when its phosphate bonds are hydrolyzed. This energy is used to drive endergonic reactions in cells.
(1) The overall flow and transformation of energy in an organism. (2) The study of how energy flows through organisms.
catabolic pathway (kat′-uh-bol′-ik)
A metabolic pathway that releases energy by breaking down complex molecules to simpler molecules.
A process by which a chemical agent called a catalyst selectively increases the rate of a reaction without being consumed by the reaction.
A chemical agent that selectively increases the rate of a reaction without being consumed by the reaction.
Energy available in molecules for release in a chemical reaction; a form of potential energy.
An organic molecule serving as a cofactor. Most vitamins function as coenzymes in metabolic reactions.
Any nonprotein molecule or ion that is required for the proper functioning of an enzyme. Cofactors can be permanently bound to the active site or may bind loosely and reversibly, along with the substrate, during catalysis.
A substance that reduces the activity of an enzyme by entering the active site in place of the substrate, whose structure it mimics.
A kind of allosteric regulation whereby a shape change in one subunit of a protein caused by substrate binding is transmitted to all the other subunits, facilitating binding of additional substrate molecules to those subunits.
endergonic reaction (en′-der-gon′-ik)
A nonspontaneous chemical reaction in which free energy is absorbed from the surroundings.
The capacity to cause change, especially to do work (to move matter against an opposing force).
In cellular metabolism, the use of energy released from an exergonic reaction to drive an endergonic reaction.
A measure of molecular disorder, or randomness.
A macromolecule serving as a catalyst, a chemical agent that increases the rate of a reaction without being consumed by the reaction. Most enzymes are proteins.
enzyme-substrate complex (en′-zīm)
A temporary complex formed when an enzyme binds to its substrate molecule(s).
exergonic reaction (ek′-ser-gon′-ik)
A spontaneous chemical reaction in which there is a net release of free energy.
A method of metabolic control in which the end product of a metabolic pathway acts as an inhibitor of an enzyme within that pathway.
first law of thermodynamics
The principle of conservation of energy: Energy can be transferred and transformed, but it cannot be created or destroyed.
The portion of a biological system’s energy that can perform work when temperature and pressure are uniform throughout the system. The change in free energy of a system (ΔG) is calculated by the equation ΔG=ΔH–TΔS, where ΔH is the change in enthalpy (in biological systems, equivalent to total energy), ΔT is the absolute temperature, and ΔS is the change in entropy.
Thermal energy in transfer from one body of matter to another.
Caused by entry of the substrate, the change in shape of the active site of an enzyme so that it binds more snugly to the substrate.
kinetic energy (kuh-net′-ik)
The energy associated with the relative motion of objects. Moving matter can perform work by imparting motion to other matter.
A series of chemical reactions that either builds a complex molecule (anabolic pathway) or breaks down a complex molecule to simpler molecules (catabolic pathway).
The totality of an organism’s chemical reactions, consisting of catabolic and anabolic pathways, which manage the material and energy resources of the organism.
A substance that reduces the activity of an enzyme by binding to a location remote from the active site, changing the enzyme’s shape so that the active site no longer effectively catalyzes the conversion of substrate to product.
phosphorylated intermediate (fos′-fōr-uh-lā′-ted)
A molecule (often a reactant) with a phosphate group covalently bound to it, making it more reactive (less stable) than the unphosphorylated molecule.
The energy that matter possesses as a result of its location or spatial arrangement (structure).
second law of thermodynamics
The principle stating that every energy transfer or transformation increases the entropy of the universe. Usable forms of energy are at least partly converted to heat.
A process that occurs without an overall input of energy; a process that is energetically favorable.
The reactant on which an enzyme works.
Kinetic energy due to the random motion of atoms and molecules; energy in its most random form. See also heat.
The study of energy transformations that occur in a collection of matter. See also first law of thermodynamics and second law of thermodynamics.
A globular protein that links into chains, two of which twist helically about each other, forming microfilaments (actin filaments) in muscle and other kinds of cells.
basal body (bā′-sul)
A eukaryotic cell structure consisting of a “9+0” arrangement of microtubule triplets. The basal body may organize the microtubule assembly of a cilium or flagellum and is structurally very similar to a centriole.
The disruption of a cell and separation of its parts by centrifugation at successively higher speeds.
A protective layer external to the plasma membrane in the cells of plants, prokaryotes, fungi, and some protists. Polysaccharides such as cellulose (in plants and some protists), chitin (in fungi), and peptidoglycan (in bacteria) are important structural components of cell walls.
In a mature plant cell, a large membranous sac with diverse roles in growth, storage, and sequestration of toxic substances.
A structure in the centrosome of an animal cell composed of a cylinder of microtubule triplets arranged in a “9+0” pattern. A centrosome has a pair of centrioles.
A structure present in the cytoplasm of animal cells that functions as a microtubule-organizing center and is important during cell division. A centrosome has two centrioles.
An organelle found in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water.
The complex of DNA and proteins that makes up eukaryotic chromosomes. When the cell is not dividing, chromatin exists in its dispersed form, as a mass of very long, thin fibers that are not visible with a light microscope.
A cellular structure consisting of one DNA molecule and associated protein molecules. (In some contexts, such as genome sequencing, the term may refer to the DNA alone.) A eukaryotic cell typically has multiple, linear chromosomes, which are located in the nucleus. A prokaryotic cell often has a single, circular chromosome, which is found in the nucleoid, a region that is not enclosed by a membrane. See also chromatin.
(plural, cilia) A short appendage containing microtubules in eukaryotic cells. A motile cilium is specialized for locomotion or moving fluid past the cell; it is formed from a core of nine outer doublet microtubules and two inner single microtubules (the “9+2” arrangement) ensheathed in an extension of the plasma membrane. A primary cilium is usually nonmotile and plays a sensory and signaling role; it lacks the two inner microtubules (the “9+0” arrangement).
A glycoprotein in the extracellular matrix of animal cells that forms strong fibers, found extensively in connective tissue and bone; the most abundant protein in the animal kingdom.
A membranous sac that helps move excess water out of certain freshwater protists.
(1) The outer region of cytoplasm in a eukaryotic cell, lying just under the plasma membrane, that has a more gel-like consistency than the inner regions due to the presence of multiple microfilaments. (2) In plants, ground tissue that is between the vascular tissue and dermal tissue in a root or eudicot stem.
(plural, cristae) (kris′-tuh, kris′-tē) An infolding of the inner membrane of a mitochondrion. The inner membrane houses electron transport chains and molecules of the enzyme catalyzing the synthesis of ATP (ATP synthase).
The contents of the cell bounded by the plasma membrane; in eukaryotes, the portion exclusive of the nucleus.
A circular flow of cytoplasm, involving interactions of myosin and actin filaments, that speeds the distribution of materials within cells.
A network of microtubules, microfilaments, and intermediate filaments that extend throughout the cytoplasm and serve a variety of mechanical, transport, and signaling functions.
The semifluid portion of the cytoplasm.
A type of intercellular junction in animal cells that functions as a rivet, fastening cells together.
In cilia and flagella, a large motor protein extending from one microtubule doublet to the adjacent doublet. ATP hydrolysis drives changes in dynein shape that lead to bending of cilia and flagella.
electron microscope (EM)
A microscope that uses magnets to focus an electron beam on or through a specimen, resulting in a practical resolution that is 100-fold greater than that of a light microscope using standard techniques. A transmission electron microscope (TEM) is used to study the internal structure of thin sections of cells. A scanning electron microscope (SEM) is used to study the fine details of cell surfaces.
The collection of membranes inside and surrounding a eukaryotic cell, related either through direct physical contact or by the transfer of membranous vesicles; includes the plasma membrane, the nuclear envelope, the smooth and rough endoplasmic reticulum, the Golgi apparatus, lysosomes, vesicles, and vacuoles.
endoplasmic reticulum (ER) (en′-dō-plaz′-mik ruh-tik′-yū-lum)
An extensive membranous network in eukaryotic cells, continuous with the outer nuclear membrane and composed of ribosome-studded (rough) and ribosome-free (smooth) regions.
The theory that mitochondria and plastids, including chloroplasts, originated as prokaryotic cells engulfed by a host cell. The engulfed cell and its host cell then evolved into a single organism. See also endosymbiosis.
eukaryotic cell (yū′-ker-ē-ot′-ik)
A type of cell with a membrane-enclosed nucleus and membrane-enclosed organelles. Organisms with eukaryotic cells (protists, plants, fungi, and animals) are called eukaryotes.
extracellular matrix (ECM)
The meshwork surrounding animal cells, consisting of glycoproteins, polysaccharides, and proteoglycans synthesized and secreted by cells.
An extracellular glycoprotein secreted by animal cells that helps them attach to the extracellular matrix.
(plural, flagella) A long cellular appendage specialized for locomotion. Like motile cilia, eukaryotic flagella have a core with nine outer doublet microtubules and two inner single microtubules (the “9+2” arrangement) ensheathed in an extension of the plasma membrane. Prokaryotic flagella have a different structure.
A membranous sac formed by phagocytosis of microorganisms or particles to be used as food by the cell.
A type of intercellular junction in animal cells, consisting of proteins surrounding a pore that allows the passage of materials between cells.
A protein with one or more covalently attached carbohydrates.
Golgi apparatus (gol′-jē)
An organelle in eukaryotic cells consisting of stacks of flat membranous sacs that modify, store, and route products of the endoplasmic reticulum and synthesize some products, notably noncellulose carbohydrates.
(plural, grana) A stack of membrane-bounded thylakoids in the chloroplast. Grana function in the light reactions of photosynthesis.
In animal cells, a transmembrane receptor protein with two subunits that interconnects the extracellular matrix and the cytoskeleton.
A component of the cytoskeleton that includes filaments intermediate in size between microtubules and microfilaments.
light microscope (LM)
An optical instrument with lenses that refract (bend) visible light to magnify images of specimens.
A membrane-enclosed sac of hydrolytic enzymes found in the cytoplasm of animal cells and some protists.
A cable composed of actin proteins in the cytoplasm of almost every eukaryotic cell, making up part of the cytoskeleton and acting alone or with myosin to cause cell contraction; also called an actin filament.
A hollow rod composed of tubulin proteins that makes up part of the cytoskeleton in all eukaryotic cells and is found in cilia and flagella.
middle lamella (luh-mel′-uh)
In plants, a thin layer of adhesive extracellular material, primarily pectins, found between the primary walls of adjacent young cells.
The compartment of the mitochondrion enclosed by the inner membrane and containing enzymes and substrates for the citric acid cycle, as well as ribosomes and DNA.
(plural, mitochondria) An organelle in eukaryotic cells that serves as the site of cellular respiration; uses oxygen to break down organic molecules and synthesize ATP.
A protein that interacts with cytoskeletal elements and other cell components, producing movement of the whole cell or parts of the cell.
A type of motor protein that associates into filaments that interact with actin filaments to cause cell contraction.
In a eukaryotic cell, the double membrane that surrounds the nucleus, perforated with pores that regulate traffic with the cytoplasm. The outer membrane is continuous with the endoplasmic reticulum.
A netlike array of protein filaments that lines the inner surface of the nuclear envelope and helps maintain the shape of the nucleus.
A non-membrane-enclosed region in a prokaryotic cell where its chromosome is located.
(plural, nucleoli) A specialized structure in the nucleus, consisting of chromosomal regions containing ribosomal RNA (rRNA) genes along with ribosomal proteins imported from the cytoplasm; site of rRNA synthesis and ribosomal subunit assembly. See also ribosome.
(1) An atom’s central core, containing protons and neutrons. (2) The organelle of a eukaryotic cell that contains the genetic material in the form of chromosomes, made up of chromatin. (3) A cluster of neurons.
Any of several membrane-enclosed structures with specialized functions, suspended in the cytosol of eukaryotic cells.
An organelle containing enzymes that transfer hydrogen atoms from various substrates to oxygen ( O 2 ) , producing and then degrading hydrogen peroxide H 2 O 2 .
A type of endocytosis in which large particulate substances or small organisms are taken up by a cell. It is carried out by some protists and by certain immune cells of animals (in mammals, mainly macrophages, neutrophils, and dendritic cells).
plasma membrane (plaz′-muh)
The membrane at the boundary of every cell that acts as a selective barrier, regulating the cell’s chemical composition.
(plural, plasmodesmata) An open channel through the cell wall that connects the cytoplasm of adjacent plant cells, allowing water, small solutes, and some larger molecules to pass between the cells.
One of a family of closely related organelles that includes chloroplasts, chromoplasts, and amyloplasts. Plastids are found in cells of photosynthetic eukaryotes.
primary cell wall
In plants, a relatively thin and flexible layer that surrounds the plasma membrane of a young cell.
prokaryotic cell (prō′-kār′-ē-ot′-ik)
A type of cell lacking a membrane-enclosed nucleus and membrane-enclosed organelles. Organisms with prokaryotic cells (bacteria and archaea) are called prokaryotes.
A large molecule consisting of a small core protein with many carbohydrate chains attached, found in the extracellular matrix of animal cells. A proteoglycan may consist of up to 95% carbohydrate.
(plural, pseudopodia) A cellular extension of amoeboid cells used in moving and feeding.
A complex of rRNA and protein molecules that functions as a site of protein synthesis in the cytoplasm; consists of a large and a small subunit. In eukaryotic cells, each subunit is assembled in the nucleolus. See also nucleolus.
That portion of the endoplasmic reticulum with ribosomes attached.
scanning electron microscope (SEM)
A microscope that uses an electron beam to scan the surface of a sample, coated with metal atoms, to study details of its topography.
secondary cell wall
In plant cells, a strong and durable matrix that is often deposited in several laminated layers around the plasma membrane and provides protection and support.
That portion of the endoplasmic reticulum that is free of ribosomes.
The dense fluid within the chloroplast surrounding the thylakoid membrane and containing ribosomes and DNA; involved in the synthesis of organic molecules from carbon dioxide and water.
A flattened, membranous sac inside a chloroplast. Thylakoids often exist in stacks called grana that are interconnected; their membranes contain molecular “machinery” used to convert light energy to chemical energy.
A type of intercellular junction between animal cells that prevents the leakage of material through the space between cells.
transmission electron microscope (TEM)
A microscope that passes an electron beam through very thin sections stained with metal atoms and is primarily used to study the internal structure of cells.
A small membranous sac in a eukaryotic cell’s cytoplasm carrying molecules produced by the cell.
A membrane-bounded vesicle whose specialized function varies in different kinds of cells.
A membranous sac in the cytoplasm of a eukaryotic cell.
The movement of a substance across a cell membrane against its concentration or electrochemical gradient, mediated by specific transport proteins and requiring an expenditure of energy.
Having both a hydrophilic region and a hydrophobic region.
A channel protein in a cellular membrane that specifically facilitates osmosis, the diffusion of free water across the membrane.
A region along which the density of a chemical substance increases or decreases.
The coupling of the “downhill” diffusion of one substance to the “uphill” transport of another against its own concentration gradient.
The random thermal motion of particles of liquids, gases, or solids. In the presence of a concentration or electrochemical gradient, diffusion results in the net movement of a substance from a region where it is more concentrated to a region where it is less concentrated.
The diffusion gradient of an ion, which is affected by both the concentration difference of an ion across a membrane (a chemical force) and the ion’s tendency to move relative to the membrane potential (an electrical force).
An active transport protein that generates voltage across a membrane while pumping ions.
Cellular uptake of biological molecules and particulate matter via formation of vesicles from the plasma membrane.
The cellular secretion of biological molecules by the fusion of vesicles containing them with the plasma membrane.
The passage of molecules or ions down their electrochemical gradient across a biological membrane with the assistance of specific transmembrane transport proteins, requiring no energy expenditure.
Limp. Lacking turgor (stiffness or firmness), as in a plant cell in surroundings where there is a tendency for water to leave the cell. (A walled cell becomes flaccid if it has a higher water potential than its surroundings, resulting in the loss of water.)
fluid mosaic model
The currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of protein molecules drifting laterally in a fluid bilayer of phospholipids.
A transmembrane protein channel that opens or closes in response to a particular stimulus.
A lipid with one or more covalently attached carbohydrates.
A protein with one or more covalently attached carbohydrates.
Referring to a solution that, when surrounding a cell, will cause the cell to lose water.
Referring to a solution that, when surrounding a cell, will cause the cell to take up water.
A transmembrane protein with hydrophobic regions that extend into and often completely span the hydrophobic interior of the membrane and with hydrophilic regions in contact with the aqueous solution on one or both sides of the membrane (or lining the channel in the case of a channel protein).
ion channel (ī′-on)
A transmembrane protein channel that allows a specific ion to diffuse across the membrane down its concentration or electrochemical gradient.
Referring to a solution that, when surrounding a cell, causes no net movement of water into or out of the cell.
The difference in electrical charge (voltage) across a cell’s plasma membrane due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances.
Regulation of solute concentrations and water balance by a cell or organism.
The diffusion of free water across a selectively permeable membrane.
The diffusion of a substance across a biological membrane with no expenditure of energy.
A protein loosely bound to the surface of a membrane or to part of an integral protein and not embedded in the lipid bilayer.
A phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall; occurs when the cell loses water to a hypertonic environment.
proton pump (prō′-ton)
An active transport protein in a cell membrane that uses ATP to transport hydrogen ions out of a cell against their concentration gradient, generating a membrane potential in the process.
A property of biological membranes that allows them to regulate the passage of substances across them.
A transport protein in the plasma membrane of animal cells that actively transports sodium out of the cell and potassium into the cell.
The ability of a solution surrounding a cell to cause that cell to gain or lose water.
A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane.
Swollen or distended, as in plant cells. (A walled cell becomes turgid if it has a lower water potential than its surroundings, resulting in entry of water.)
prokaryotes use substances other than oxygen as reactants in a similiar process that harvest chemical energy without oxygen